(1) Field of the Invention
The present invention relates to controlling the relative velocities and positions of a pair of moving objects and particularly to synchronizing the movements of a parallelly movable tool with the movements of workpieces traveling on a continuously operating conveyor. More specifically, this invention is directed to a sensor for use in controlling the speed and position of a first mechanism relative to a moving object and to a control system utilizing such sensor. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited to use in controlling a foundry operation and particularly the pouring of molten metal into moving molds. A summary of the state of the art with respect to the pouring of molten metal into spatially displaced molds traveling on a preferably continuously operating conveyor may be found in U.S. Pat. No. 2,522,031. In view of the obvious and numerous disadvantages of prior art apparatus such as that discussed in U.S. Pat. No. 2,522,031 such apparatus has achieved only limited utilization and success in pouring machines for traveling mold conveyors in the United States. Nevertheless, there has been a long-standing desire in the art for such apparatus in view of its substantial utility in the production of many consumer products such as, for example, engine blocks for motor vehicles.
The principal deficiency of prior art pouring machines has resided in the area of control where an accurate and reliable mechanism for obtaining and maintaining synchronized speed and a desired relative position between the pouring machine and the traveling molds has not previously been available. Thus, by way of example, prior attempts to sense mold position by establishing mechanical contact therewith have been characterized by lack of reliability and serviceability; the sensors being particularly susceptible to damage incident to "breakaway" as accompanies overtravel between the mold and pouring machine. Also, prior art controls for synchronizing pouring machine and mold speed have been comparatively costly. While prior art electronic controls have had the capability of synchronizing the speed of the pouring machine to that of the conveyor on which the molds to be poured were traveling, such electronic controls have been insensitive to position variations incident to the always present oscillations of the conveyor; such oscillations resulting in the speed of the mold varying about that established by the conveyor drive motor. Attempts to overcome this problem of position insensitivity have resulted in complex controls, some of which have had a tendency to "hunt".